In order to improve environmental pollutions due to disposable bowl made of foamable synthetic resin, plastics and aluminum foil, etc., there have been studies on biodegradable disposable bowl comprising natural polymers such as paper and starch, etc. which can be decomposed after filled in ground.
Since said disposable bowl is biodegradable contrary to such disposable bowl made of synthetic resins etc., it does not cause environmental pollutions and can be easily processed.
However, an inner or outer part of the biodegradable disposable bowl can be polluted with pathogenic Escherichia coli, O-157, pseudomonas aeruginosa, staphylococcus and salmonella, etc. In addition, since the biodegradable disposable bowl can be decomposed by microorganism, it has a very weak preservative property. Further, the biodegradable disposable bowl has a poor impact resistance compared to that of the prior plastic bowl.
Accordingly, there were known several techniques for adding the impact resistance, antibiosis and preservative property, etc. to the biodegradable disposable bowl.
For example, Japanese Patent Publication No. Hei 8-311243 discloses a biodegradable foamable composition having improved antibiosis, antifungal property and impact resistance, which is made by combining starch based polymers, vegetable fibers, metal ions, foaming agent and aliphatic polyester.
However, such a method for preparing a biodegradable disposable bowl according to the prior art still has problems that the bowl has a poor long-term preservative property due to a decomposition by microorganism etc. particularly when it is used for storing foods and the sterilizing and deodorizing properties of the bowl are deficient.
On the other hand, the prior biodegradable disposal bowl has low production efficiency due to its poor releasing property.
That is, when preparing the biodegradable disposable bowl according to the prior art, the bowl is not easily released from a mold in case that a depth of the bowl is 5 cm or more. As a result, it is required to manually release the bowl one by one from the mold after discontinuing the preparing process, which lower the production efficiency.